have you ever tried the inspection camera and the pressure tester at the same time on the warm block?

 

Kevin,

I haven't confirmed because I decided not to take the engine apart but after a good deal of research and talking to a few folks in town who have dealt with Rover engines a lot I think the root cause is a small crack in the block by the head bolt behind the #4 cylinder liner.

A few articles I looked at were here:

JE Robison Service — the blog: Should You Rebuild or Replace Your Land Rover V8?

JE Robison Service — the blog: The last word on Land Rover liner failures - I hope!



EVN mentioned earlier in this thread that he thought the root could be a crack in the head. I thought about pulling everything apart and called the local machine shop to price out getting the heads machined flat after a HG job along with checking them for cracks. The guy I talked to said that he thought it was unlikely given that he hadn't run into any cracked heads (many warped heads from overheating issues, but no cracked ones) in the 100's of jobs he'd done on Rover V8s for the local LR dealer.

Either way, I settled on the fact that I think it's a crack in the block behind the cylinder liner, which according to Robinson Service and a few other things I read seems to be more common in the 4.6 version, especially near the head bolts that sit close to the #4 cylinder head.

I'm not getting any of the tell tale "diesel" sounds that would indicate a slipped liner, and the coolant leak that I had was very slow -- probably less than 1/2 of the reservoir over 2-3 fill ups (~800 miles?), so the cylinder isn't "steam cleaned".

I decided that tearing down the engine and ripping out the cylinder sleeves to confirm the block was trashed would probably be an expensive and frustrating exercise in futility, and decided against the HG job (since the truck runs fine otherwise, and the coolant pressure test held without issue when the truck was cold even with the #4 plug removed). I did a bit more poking around and found that some of the guys who are using old Buick V8s that our engines are based on in their rat rods/hot rods have had some luck with block sealer to fix cracks in the block.

So I decided to try that route. My reasoning was that if the block sealer could "seal" a tiny crack behind the cylinder wall, it might be a somewhat permanent fix. I'm (quite obviously) not an expert, but I reasoned that since the crack was behind the cylinder liner, the pressures might be lower than on the head gasket area, which would increase the probability of the block sealer actually holding over the longer term.

I settled on trying some Bar's Leaks HG-1. I was pretty skeptical on whether this would work anyway, so I went with the Bar's leaks product since it is a fairly recently developed formula and it would allow me to just add it directly to the coolant, instead of having to do a full flush first, which is a requirement with some other block sealers on the market.

I followed the directions to the letter when I put it in, ran the truck for about 150 miles with the full bottle of HG-1 in the coolant, and it has completely fixed the misfire issues.

After about 150 miles and 20-25 successful cold and hot starts, I did a full coolant flush (dump coolant, flush radiator with hose, flush system with hose, run distilled till it's hot, let cool, flush that out, refill with coolant) to get the excess HG-1 out (which turned the coolant quite sparkly) and the truck has been running fine since. I have put about 500 miles on it since the repair, and haven't noticed any additional coolant loss.

Did it work? I seems so. I'd be lying if I said I was confident that it's a permanent fix however, so I am monitoring it closely.

Just as an FYI, I am running a Motorad 180 degree thermostat, and am seeing temps of 198 or so at 70 on the highway (100 degree Central Texas heat in traffic) and about 204-206 in town. Before flushing the coolant and after the HG-1, my temps climbed up to about 215-218 in town, which is one of the reasons I decided to flush the cooling system.


Also -- I did try the "paper towel" test (rolled up paper towel through the spark plug hole) to see if the injectors would leak down fuel or coolant, but the test didn't turn anything up, even when running a coolant pressure test with the spark plug removed -- which is why I leaned away from leaky injectors being the root cause of my issue.

Drowssap -- I have not run a pressure test on a hot block, because I was afraid of making a mistake and scalding myself with hot coolant. I did run the inspection camera and tried a paper towel test on a warm block after pulling the plug (not hot, had been sitting for about 30-40 min) and it didn't turn up anything new or different. None of the telltale coolant leak signs like a "steam cleaned" cylinder head, etc.

I hope this helps, and I'd be interested to hear how you make out.

 

Glad that it's working and holding up.
Haven't had any issues with mine either since the fix and it's been over 50k miles.